1. Field of the Invention
The present invention relates to a disk cartridge comprising a casing formed by combining a pair of half casings made of a resinous material and a disk-like recording medium such as a magnetic disk, an optical disk received in the casing.
2. Discussion of Background
A floppy disk has widely been used as an exchangeable information storage medium which can be fitted to a magnetic recording/reproducing device and can be removed from it or storage or transportation in the same manner as a magnetic tape cassette and a disk pack. 8-inch and 5-inch floppy disks have generally used. For such floppy disks, a thin flexible jacket made of vinyl chloride or the like is used as a casing to protect a magnetic disk. However, the mechanical strength of the jacket is too weak to provide sufficient protection to the magnetic disk. Since a part of the magnetic disk is exposed outside, careful attention has to be paid so as to prevent dust from being deposited on the magnetic disk. For instance, a conventional 3.5-inch floppy disk employs a casing which is formed by combining upper and lower half casings made of a resinous material by means of connecting ribs formed on the base surface of at least one of the half casings wherein each of the half casings has an outer circumferential wall at the circumference of the base surface and an annular rib for defining a magnetic disk rotating region, formed at the inner portion of the outer circumferential wall, and other necessary ribs. Such casing is strong and difficult to deform because the casing is made thick. Further, a shutter is provided at a window formed in the casing through which a magnetic head is inserted and a hub which is provided at the side of a magnetic disk is inserted into another window formed in the casing through which the magnetic disk is driven.
However, in the conventional disk cartridge, not only the connecting ribs but also other ribs formed in either of the half casings are made to contact with the other half casing. Accordingly, there is a problem that dust is apt to produce inside the casing although dust is prevented from entering from the outside of the casing. Generally, connection of the connecting ribs projecting from one of the half casings to the other half casing is carried out by applying ultrasonic vibrations to the portions to be connected to melt-bond those portions. At the moment, the mutually contacting surfaces are rubbed and a portion of the half casings are shaved to thereby generate resin powder. In particular, when ultrasonic vibrations are applied to a connecting rib or a portion near the rib, the vibrations are transmitted to the other ribs. Since the free end of the connecting ribs is formed to be slightly higher than the other ribs so as to fuse that portion, the connecting rib first comes to contact with the other half casing, and when the contacting portion of the connecting rib is fused by the application of the ultrasonic vibrations, the other ribs come to contact with the other half casing. Accordingly, an amount of the resin powder is much in the vicinity of the connecting ribs and is small in the vicinity of the other ribs. However, since the annular rib, among other ribs, formed at the inner portion of the base surface of the half casings is formed at the outer circumference of the magnetic disk, the area of contact is large, and therefore a much amount of the resin powder is produced. Further, since the annular rib is formed near the magnetic disk, there may be caused erroneous recording or reproducing if the resin powder deposits on the magnetic disk.
The inventor of this application proposed a disk cartridge as in Japanese Utility Model Application Nos. 151416/1988 and 151417/1988 wherein an annular rib which defines a magnetic disk rotating region is formed in one of the half casings so as not to contact with the other half casing to thereby suppress production of the resin powder. In the above-mentioned second application, the inventor proposed a disk cartridge having reinforcing ribs which are formed on the base surface at the portion near the outside of the annular rib so as to provide rigidity required for the casing, the reinforcing ribs being formed so as to contact with the other half casing. In such disk cartridge, it is necessary to form a gap between the annular rib and the other half casing as possible so that dust does not enter into the magnetic disk rotating region. However, when the gap is formed at the same level from the base surface, the magnetic disk is apt to enter in the gap. Accordingly, the annular ribs of the upper and lower half casings are formed so that they cooperate to form a circular circumferential wall, and at least one projection and recess are formed in the main portion of the annular ribs so that the projection and the recess are fitted to each other.
The above-mentioned construction will be described with reference to FIG. 6. The main portion of an annular rib 12 is formed in an upper half casing 10 so that the level of the free end of the annular rib 12 is substantially the same height from the base surface 14 of the upper half casing 10. Further, projections 16 (16a, . . . 16d) are respectively formed at the four corner portions of the base surface 14 of the upper half casing 10. Similarly, as shown in FIG. 7, the main portion of an annular rib 20 is formed oh the base surface 22 of a lower half casing 18, which is paired with the upper half casing 10, so that the level of the free end of the annular rib 20 is substantially the same height from the base surface 22. Further, recesses 24 (24a, . . . 24c) are respectively formed at the four corner portions of the base surface 22 of the lower half casing 18. The positions of the recesses 24 are determined so as to correspond to those of the projections 16. Gaps 26 (26a, 26b) having a dimension as large as 2 mm are formed at both sides of a projection 16 which is to be fitted to one of the four fitting portions in the casing when the upper and lower half casings are combined as shown in FIG. 8. This gap is necessary in the consideration of precision of machining metal dies for molding the half casings and the fluctuation of molded products. In the conventional disk cartridge, dust is apt to enter into a magnetic disk rotating region through the gap 26 at the fitting portion of the projection 16 and the recess 24. The other gap 28 formed between other ribs and a half casing is as small as about 0.1 mm, and it does not cause a serious problem.